The present invention relates to a control system for controlling an output torque of an internal combustion engine of motor vehicles through control of a throttle valve of the engine.
Conventionally, in order to prevent hunting (vehicle resonance) of the motor vehicle occurring at the time of acceleration, a throttle valve is driven so as to decrease the output torque of the internal combustion engine such as disclosed in the Japanese Patent Provisional Publication No. 60-178940. In addition, in motor vehicles with an automatic transmission (A/T vehicles), lock-up control is executed with the input and output of a torque converter being mechanically coupled to each other. Such an arrangement allows the prevention of the hunting, while providing a problem in acceleration performance because the rising speed of the engine torque becomes dull from the intitial stage when depressing the acceleration pedal. For instance, for resolving this problem, the throttle valve can compulsorily and reversely be operated in the closing direction at the time of accelerating operation to thereby control the engine torque to meet the requirement of the transient response concurrently with preventing the hunting occurring at the time of the transition. However, in the conventional lock-up control, the execution is in practice prohibited at the time of a low-speed running state and an accelerating or decelerating operation because of increasing the vehicle vibration and vehicle shock. Thus, the lock-up-allowable region becomes narrower so as to deteriorate the fuel consumption reducing effect. In addition, there is a problem that the air flow meter overshoots in response to the acceleration so that its detection value becomes greater so as to excessively increase the fuel injection amount, thereby similarly deteriorating the fuel consumption.